JPH07123168B2 - Photoelectric element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photoelectric element, and more particularly to an optical reading element having an amorphous silicon layer as a photoconductive layer for image reading in a copying machine, a facsimile machine or the like. .

(Prior Art) Conventionally, 0.1 to 100 ppm is present in a photoconductor or an amorphous silicon (hereinafter referred to as a-Si) layer as a photoelectric conversion layer of a solar cell.
Boron (B) is doped. The optimum value of the doping amount is determined from the photoelectric characteristics and deterioration characteristics of each device. By doping B, the resistance of the a-Si layer is increased, and as a result, photoelectric characteristics are improved and deterioration is prevented.

However, in the photoconductive type optical reading element which is the main object of the present invention, the above doping amount of B cannot be applied. This is because the resistance value during light irradiation is too high to correctly detect the photocurrent as a signal. On the other hand, undoped a-Si
Has a drawback that it has a high resistance when exposed to light, that is, causes half-deterioration due to the characteristics of its structural properties. One of the causes of this photodegradation development is the influence of H ₂ O, O ₂ , N _{2 and the} like that enter the film during a-Si pattern formation. It is considered that when the (OH) group or O, N atom is bonded to the Si atom in the film, a dangling bond (unpaired electron pair) is generated as shown in FIG. The doping of B is intended to suppress the generation of dangling bonds due to the above-mentioned impurities, and this is generally called compensation. FIG. 4 shows this situation. B
If the doping amount is too large, p-type conduction is exhibited, and there is almost no suitable electrode, which is a problem.

From the above, in the optical reading element using the a-Si layer as the photoconductive layer, the required characteristics cannot be obtained with a B-doping amount of 0.1 to 100 ppm, and there is a problem that photodegradation is large in the non-doping. .

(Object of the Invention) The present invention solves the above-mentioned problems of the prior art. Therefore, a photocurrent can be obtained without increasing the resistance value of the photoconductive layer, and the photodegradation is reduced. The present invention provides a photoelectric conversion element of a conductive type, especially an optical reading element.

(Structure of the Invention) In order to achieve the above object, the present invention provides an active layer
The a-Si layer is doped with boron in the range of (10 ¹³ to 10 ¹⁵ ) / cm ³ .

FIG. 1 shows the relationship between the B doping amount and the photocurrent. From this figure, the B doping amount is B ₂ H ₆ / SiH ₄ (ppm),
^-1 to 10 ^-3 ppm is suitable. In particular, in the range of 10 ^-2 to 10 ^-3 ppm, the current value is not inferior to that in the non-doped case, which is preferable. The film formation conditions at this time were as follows: SiH ₄ flow rate: 10 scc
m, power; 10 W, pressure; 0.1 Torr, B ₂ H ₆ / H ₂ ; flow rate change depending on doping conditions, substrate temperature; 300 ° C. B ₂ H ₆ / SiH ₄
FIG. 2 shows the results of SIMS evaluation of the amount of B actually doped in the film with respect to the flow rate (ppm). From now on, 10 ^-1
The amount of B doped in the film with respect to B ₂ H ₆ / SiH _{4 of} ˜10 ⁻³ ppm corresponds to (10 ¹⁵ to 10 ¹³ ) / cm ³ , and the preferable B doping amount is (10 ¹⁴ to It can be said that it is 10 ¹³ ) / cm ³ .

The lightly doped B plays a major role in reducing photodegradation of the a-Si film. Comparing the photo-deterioration between a B-doped sample of about 10 ¹³ / cm ³ and a conventional non-doped sample,
As shown in FIG. 5, it can be seen that the doped sample has a higher residual rate (smaller photodegradation). In this case, the light irradiation is continuous irradiation by a green light source (λ = 550 nm).

(Effects of the Invention) As described above, according to the present invention, the a-Si layer as the photoconductive layer, necessary by doping boron in the range of (10 ¹³ to 10 ¹⁵ ) / cm ³ , A photocurrent can be obtained and photodegradation can be reduced, and an optical reading element that is sufficiently suitable for actual use in a copying machine, a facsimile machine, or the like can be realized.

[Brief description of drawings]

Figure 1 shows the doping amount of B (B ₂ H ₆ / SiH ₄ pp in the a-Si film).
m) and photocurrent, Fig. 2 shows B ₂ H ₆ / SiH
₄ is a diagram showing the amount of B doped in the film with respect to the flow rate of ₄ (ppm), FIG. 3 is a diagram showing a dangling bond which is one of the causes of photodegradation, and FIG. 4 is an effect of B doping. And FIG. 5 are diagrams showing the photodegradation characteristics of the B-doped sample and the non-doped sample.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Tani 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP 59-54275 (JP, A) JP 59 -29157 (JP, B2)

Claims (2)

[Claims] 1. A photoconductive photoelectric device using an amorphous silicon layer as an active layer, wherein the amorphous silicon layer is doped with boron in a range of (10 ¹³ to 10 ¹⁵ ) / cm ^3. Photoelectric device that does. 2. A photoconductive reading element is constituted by using an amorphous silicon layer doped with boron in a range of (10 ¹³ to 10 ¹⁵ ) / cm ³ . The photoelectric device according to item 1).